[求助]大全 677

677.        Sunspots, vortices of gas associated with strong electromagnetic activity, are visible as dark spots on the surface of  the Sun but have never been sighted on the Sun’s poles or equator.

(A) are visible as dark spots on the surface of the Sun but have never been sighted on

(B) are visible as dark spots that never have been sighted on the surface of the Sun

(C) appear on the surface of the Sun as dark spots although never sighted at

(D) appear as dark spots on the surface of the Sun, although never having been sighted at（C）

(E) appear as dark spots on the Sun’s surface, which have never been sighted on

不懂为什么选C

B.Changing the modifying clause so
that that never...Sun distorts the
meaning of the sentence; the contrast is lost

C.Although typically introduces a subordinate clause, which has a
subject and a verb, but here there is no subject
and sighted is not a complete verb

D.Although usually introduce a subordinate clause, but there is no
subject of the clause and having been
sighted is not a complete verb phrase

E.The relative pronoun which
should immediately follow its referent; here which illogically follows surface,
and its intended referent, either sunspots
or dark spots, becomes unclear

看来要好好看看OG了，呵呵，非常感谢!

C.Although typically introduces a subordinate clause, which has a subject and a verb, but here there is no subject and sighted is not a complete verb

记得although、though等后面主谓可以省，如果此处为although (they are) sighted...

不明白的是为何用完成时，如果非用完成时，那么although后就不可以省